DHX Select model features both the robust and trouble-free Direct Coil heating system and Advanced Flow Control. Stiebel Eltron's most advanced water heating technology, the Direct Coil heating system is self-cleaning for superior limescale resistance. Advanced Flow Control, patented in Germany, is exclusive to Stiebel Eltron tankless heaters. If hot water demand exceeds working capacity, Advanced Flow Control automatically maintains consistent temperatures by slightly reducing flow. Ideal for residential and commercial point-of-use sink applications, DHX plus models heat water endlessly on demand at 99% efficiency. They have no stand-by energy losses because they do not store hot water like tank water heaters. No venting is required, and the compact European design can be installed with the unit visible. The DHX series excels at supplying water at a constant temperature, but the amount of hot water and its temperature depends on the incoming cold-water temperature and the size of the DHX model. The correct model size must be chosen by using the DHX Sizing Guide or by calling Stiebel Eltron at 800.582.8423. Stiebel Eltron invented electric tankless water heating almost 100 years ago, and is still the industry pioneer and world leader, with an engineering and manufacturing tradition of excellence.